In ignition systems of the type to which the present invention relates, an ignition coil has a controlled switch connected in the primary circuit thereof, the secondary being connected to one or more spark plugs, preferably through a distributor. An ignition control element, for example an inductive transducer, controls the operation of the controlled switch to pass current therethrough and charge the ignition coil. The controlled switch is closed at a predetermined instant of time, causing rapid rise of current through the ignition coil which will terminate in a saturation current if the switch remains closed for a long enough period of time. Upon opening of the switch, the secondary voltage provides a pronounced voltage kick which has a high enough voltage to cause breakdown of the spark gap of the spark plug if the ignition system is connected to an internal combustion engine, for example of the automotive type. The transducer provides an ignition signal at a predetermined time with respect to an operating state of the internal combustion (IC) engine, for example with respect to the upper dead center (UDC) position of a piston thereof. Suitable ignition timing circuits or other arrangements can be used to shift the ignition signal to provide for advance or retard of the spark with respect to the UDC position of the piston in accordance with various operating or environmental parameters of the internal combustion engine. The ignition timing signal not only controls closing of the switch but primarily controls opening thereof at a predetermined timing instant. A dwell angle control arrangement is provided to close the switch at a proper time so that sufficient current can flow through the coil to store magnetic energy therein, so that the coil will be essentially in saturation and provide, at the proper ignition instant, the full magnetic energy to the spark gap, typically a spark plug. Dwell angle control systems have been previously described, see, for example, the cross-referenced U.S. Pat. No. 3,881,458 (to which German Disclosure Document DT-OS 2,244,781 corresponds). Such ignition systems have a disadvantage, however, in that it is possible that the spark may be too weak or too short, resulting in insufficient or incomplete combustion of the fuel-air mixture in the IC engine. In the limiting case, a misfire may occur, resulting in no combustion of the mixture at that time at all.
It has been proposed to ensure ignition of the fuel-air mixture in the respective cylinder by providing a spark train, that is, a plurality of firings for each ignition event, occurring rapidly, one after the other. Sequential ignition pulses are generated by enabling a frequency generating to provide a pulse train to a control switch connected to the spark plug, at any ignition event, or with respect to any ignition instant, so that the coil will then provide a pulse train to the spark plug. This system has a disadvantage in that the frequency generator will provide control for the coil of the spark plug only after the ignition instant. Thus, the switch must first close to store magnetic energy in the ignition coil so that, upon subsequent opening, a spark impulse is delivered therefrom to the spark plug. The first firing or arc-over of the spark plug thus occurs at a period of time which is delayed with respect to the actually desired ignition instant.